The present invention relates generally to gas turbine engines, and, more specifically, to fuel systems therein.
A gas turbine engine includes a compressor which provides pressurized air to a combustor wherein it is mixed with fuel and ignited for generating hot combustion gases which flow downstream to one or more turbines which extract energy therefrom for powering the compressor and providing useful work such as powering an aircraft in flight. Two significant design objectives in an aircraft engine are fuel consumption and exhaust emissions. Aircraft engines continually undergo development for reducing fuel consumption or specific fuel consumption (SFC). And, since the engines produce exhaust emissions during flight, it is also desirable to reduce those emissions, including in particular NOx emissions which adversely affect atmospheric ozone.
The fuel is injected into the combustor using fuel injectors which take various forms and complexity for suitably atomizing the fuel for being mixed with air. The pressurized air provided by the compressor is introduced into the combustor through air swirlers which take various forms and provide one or more concentric air flowpaths around the injected fuel to provide a suitably mixed fuel and air mixture.
It is desirable to obtain concentricity of the swirled air around the injected fuel in all power levels of operation of the engine to maximize fuel and air mixing effectiveness for decreasing both SFC and NOx emissions. However, the fuel injectors are typically suspended from a combustor case, and the air swirlers are typically mounted to the combustor suitably supported inside the combustor case. These components are operated at different temperatures throughout the entire operating envelope of the engine, and are typically made from different materials which cause differential thermal expansion and contraction therebetween. Off-center fuel injection into the swirlers results in undesirably higher SFC and increased NOx emissions, and may also decrease the useful life of the swirlers themselves due to increased operating temperature thereof.
Alignment of the fuel injectors and the swirlers is also affected by the initial assembly of these components in the engine. The fuel injectors and swirlers are individually manufactured and are therefore subject to typical manufacturing tolerances causing random size variations from injector to injector and from swirler to swirler. And, the individual injectors and swirlers must be assembled into a complete assembly and are therefore also object to manufacturing stack-up tolerances which also affect the alignment between the individual fuel injectors in their respective air swirlers.
Accordingly, alignment inaccuracies between respective ones of fuel injectors and swirlers are inherently created in typical gas turbine engine combustors and adversely affect both SFC and NOx emissions. It is therefore desirable to improve the alignment between fuel injectors and their corresponding swirlers for improving both SFC and NOx emissions.